In general, all optimizations are good for energy, because of you finish faster, you use less energy.

That’s more if you believe in “race to idle/sleep,” where you finish bursty tasks as quick as possible. Unfortunately, without a fascistic scheduler, I don’t think it works in practice. There’s always going to be that little thing that pushes the CPU at 0.1% because it doesn’t poll properly, or a web page is going to hammer the hell out of your CPU, and GPU for good measure.